Stator and electric motor including the same

Abstract

A stator may include a back iron having a cylindrical shape and extending along an axial direction; a plurality of teeth provided on an inner circumferential surface of the back iron; and a stator coil provided on the plurality of teeth. A plurality of coolant passages may be arranged in a circumferential direction in circumferential regions of the back iron and the plurality of coolant passages may extend along the axial direction to a first end face of the back iron. The plurality of coolant passages may include a coolant passage located in an uppermost portion of the back iron in a vertical direction and a coolant passage located in a lowermost portion of the back iron in the vertical direction. At the first end face of the back iron, an arrangement of the plurality of coolant passages may have two-fold symmetry and may not have four-fold symmetry.

What is claimed is: 
     
         1 . A stator for an electric motor, comprising:
 a back iron having a cylindrical shape and extending along an axial direction;   a plurality of teeth provided on an inner circumferential surface of the back iron; and   a stator coil provided on the plurality of teeth,   wherein   the back iron comprises a plurality of coolant passages that is arranged in a circumferential direction in circumferential regions of the back iron, the plurality of coolant passages extending along the axial direction to a first end face of the back iron,   the plurality of coolant passages includes a coolant passage located in an uppermost portion of the back iron in a vertical direction and a coolant passage located in a lowermost portion of the back iron in the vertical direction, and   at the first end face of the back iron, an arrangement of the plurality of coolant passages has two-fold symmetry and does not have four-fold symmetry.   
     
     
         2 . The stator according to  claim 1 , wherein
 the plurality of coolant passages comprises:   a plurality of first coolant passages disposed in a first circumferential region of the back iron;   a plurality of second coolant passages disposed in a second circumferential region of the back iron, and   the first circumferential region includes the uppermost portion and the second circumferential region includes the lowermost portion.   
     
     
         3 . The stator according to  claim 2 , wherein the uppermost portion is located at a center of the first circumferential region and the lowermost portion is located in a center of the second circumferential region. 
     
     
         4 . The stator according to  claim 2 , wherein each of the first circumferential region and the second circumferential region is a region of 120 degrees or less in the circumferential direction. 
     
     
         5 . The stator according to  claim 4 , wherein each of the first circumferential region and the second circumferential region is a region of 45 degrees or less in the circumferential direction. 
     
     
         6 . The stator according to  claim 2 , wherein none of the plurality of coolant passages is disposed in a third circumferential region and a fourth circumferential region of the back iron, each of the third circumferential region and the fourth circumferential region is adjacent to the first circumferential region and the second circumferential region. 
     
     
         7 . The stator according to  claim 1 , wherein the plurality of coolant passages is at least partially formed of a plurality of through holes defined in the back iron. 
     
     
         8 . The stator according to  claim 1 , wherein the back iron comprises an annular coolant passage extending in the circumferential direction and connected to each of the plurality of coolant passages. 
     
     
         9 . The stator according to  claim 8 , wherein the annular coolant passage is formed of a groove defined in an outer circumferential surface of the back iron. 
     
     
         10 . The stator according to  claim 8 , further comprising a casing surrounding an outer circumferential surface of the back iron,
 wherein the casing comprises a coolant supply hole connected to the annular coolant passage, the coolant supply hole located at an intermediate position of the annular coolant passage in the vertical direction.   
     
     
         11 . The stator according to  claim 1 , further comprising a first annular member disposed on the first end face of the back iron,
 wherein the first annular member comprises a plurality of first coolant injection holes that are directed toward a first coil end of the stator coil protruding from the first end face.   
     
     
         12 . The stator according to  claim 1 , wherein the plurality of coolant passages extends along the axial direction to a second end face of the back iron located opposite the first end face. 
     
     
         13 . The stator according to  claim 12 , further comprising a second annular member disposed on the second end face of the back iron,
 wherein the second annular member comprises a plurality of second coolant injection holes that are directed toward a second coil end of the stator coil protruding from the second end face.   
     
     
         14 . An electric motor comprising:
 the stator according to  claim 1 ; and   a rotor disposed within the stator.